The long-term objectives of this project are to identify and characterize the forces that underlie chromosome movement in meiosis and mitosis, including interactions of chromosomes with the spindle and microtubule dynamics involved in spindle assembly and function. The proposed studies focus on ncd, a Drosophila protein related to the microtubule motor protein, kinesin. Ncd is a minus-end microtubule motor required for normal chromosome segregation in oocyte meiosis and mitosis in early embryos. The ncd protein is associated with meiotic spindles and mitotic spindle fibers and centrosomes. The proposed studies will test the hypotheses that 1) ncd functions to assemble bipolar spindles in meiosis and move chromosomes poleward in meiosis and mitosis, and 2) interactions of ncd with microtubules during its mechanochemical cycle differ from those of kinesin, and account for the differences in motility properties of ncd and kinesin. Specific aims are to: 1. Visualize spindle assembly and chromosome movement in wildtype and mutant oocytes and embryos using transformants carrying the A. Victoria green fluorescent protein (GFP) fused to ncd. 2. Screen for and analyze new modifier mutants of ncd to identify proteins that interact with specific ncd mutant alleles. 3. Determine the tubulin subunit(s) to which ncd binds and the site(s) of binding using genetic interactions of ncd with tubulin mutants, molecular analysis, and in vitro binding studies. 4. Design, construct and analyze mutants that specifically affect the ncd ATPase in order to obtain information regarding interactions of the ncd motor with microtubules. The proposed studies address the basis of chromosome movement during meiosis and mitosis, and the role and mechanism of function of the ncd microtubule motor protein. Results of these studies will provide information regarding the molecular forces needed for proper chromosome distribution in dividing cells. Defective chromosome distribution causes aneuploidy and genetic abnormalities, and is associated with cellular transformation in humans.